The Sibling Experience
by RenaRoo
Summary: Damian desperately attempts to not be charmed by his sister and niece.


Anonymous prompted: Could you write a little something with Cass, Damian and Mar'i Grayson bonding?

Batman and related properties © DC Comics  
story © RenaRoo

 **The Sibling Experience**

"And just _what_ would be the point of this exercise, Cain?"

There was a certain lilt in Damian's words that Cassandra was growing better at recognizing. There was a definite sense of expectation from his words – and Damian _did_ love his words, the bigger and more complicated the better when talking to his newly adopted sister – that Cass would not be able to follow his meaning.

But she smiled at him all the same, holding the baby in her arms lovingly against her chest.

"Shh," she told him instead.

Damian's nose wrinkled. It did that a lot, like he smelled something foul when he really wasn't. It was a cute face, and Cass liked to pinch his cheeks when he did it to annoy him.

She knew that he was making that face out of disgust, but disgust with what? Not being sure? Not being kept "in" on whatever it was that Cass had planned.

It could have easily been anything, but Cass suspected it was more about Mar'i.

"You're holding her head wrong," Damian growled, reaching for the baby yet again.

Cass turned so that Damian touched her shoulder rather than their new niece. It made him let out another low growl and flatten on the ground beside her.

"Wait," she instructed the no-longer-youngest Wayne.

He gave her a grouchy look in response but kept his mouth closed, leaning on his hands as he watched Cass expectantly.

Able to give her full attention to Mar'i once more, Cass looked into the young baby's bright green eyes. As she pulled back, Mar'is eyes widened and her smile grew, chubby fingers reaching for the drawstrings of Cass' hoodie.

Mar'i let out a long string of babbling and drool as she tried desperately to reach for Cassandra.

Cass smiled back at the baby and slowly began tilting her further and further back. Giggles began erupting from the child as she reached and kicked in response to her body being tilted more toward Cass' lap.

Damian, curiosity piqued, was on his knees and arching to look over Cass' shoulder. His eyes were widening at the sight of Mar'i seemingly dangling in the air just above Cass' knees.

"Hey! That's not safe! Cain! Don't hurt the baby!" he sputtered, face heating up with anxiety and worry. "I mean it, Cain! _Stop!_ I will not hesitate to call Grayson and let him know what you are doing to the child!"

"You care?" Cass asked, intrigued. "About baby?"

"Of course not!" Damian spat.

As Mari's body wiggled upside down, Damian jerked nervously toward her, ready to dive and take the baby away from Cass.

Knowingly, Cass smiled and quickly pulled the baby back upright and against her. Such a small motion, so controlled, but Mar'i squealed and wailed happily, hands popping up and down while her feet kicked.

The baby's laughter was infectious and Cass joined in, rubbing her cheek against the baby's. But she didn't close her eyes, a knowing smirk on her face as she watched Damian twitch with a hint of jealousy.

Cass repeated the motion, a little swifter each time now that Mar'i knew what was happening with their play and was expecting the quick rise back to her upright position.

Though her arms were far from sore, Cass turned to Damian more directly and began to reach him Mar'i.

The preteen recoiled back from the little princess. "What–"

"Your turn," Cass informed him.

The younger Wayne tried to pullback more but Cassandra was already in the process of dumping Mar'i into his arms.

"I don't _want–"_ Damian trailed off into a flustered noise as Mar'i, already riled up by Cass' play, was bapping at his cheeks with her tiny hands. He huffed which only encouraged fingers getting stuck between his lips.

"Play," Cass ordered, taking her turn to stretch out over the floor and watch with bemusement.

"You're the worst," Damian announced, doing his level best to tilt Mar'i back and forth, a little more erratic than Cass' own methods. But Mar'i was enjoying it immensely, high pitched squeals bubbling out of her.

Cassandra watched the ghost of a smile cross her brother's face before returning it with one of her own.

"I know," she finally answered, a laugh in her chest.


End file.
